The present invention relates to chronically-implantable electrical leads for intravascular delivery of electrodes. More particularly it relates to a multi-electrode intravascular lead, designed for use in coronary veins and venules.
Chronically-implantable leads for intravascular delivery of electrodes to be positioned in the coronary veins must be of small diameter (typical dimension  less than 4 French), to enable effective catheterization of the Smaller venules. In addition, leads for intravascular or intracardiac chronic implants must be flexible enough to withstand the harsh cyclic loading conditions to which they are exposed. For this reason, these leads are usually constructed with one or more wire coils that impart the lead its desirable mechanical properties. For the purpose of electrically controlling the cardiac muscle, as described by Ben-Haim et al. (PCT/IL97/00012) leads must present low resistance (or low impedance in AC systems) to electric currents in order to be effective. Resistance however is a function of material properties (bulk resistivity), cross-section of the conductor and the conductor""s length. As such, the long, thin wires needed for the construction of very thin leads, and that results in high resistance values, which are highly inefficient for their use with implantable electrical muscle controllers.
For example, prior art 20 cm long, 3 to 4 French wide tetrapolar leads, having MP35N coated wires, forming parallel coils have terminal-to-electrode resistance values ranging from 150 Ohms to 200 Ohms. At the same time, typical electrodes for electrical muscle control have ionic conduction impedances of approximately 150 Ohms. As such, the wire resistance accounts for energy loss of as much as half the energy that could otherwise be delivered to the tissue.
Multipolar leads for permanent implant in the coronary veins are well known and are in current use for left-ventricular pacing. Daubert et al. (J. C. Daubert, P. Ritter, H. LeBreton, D. Gras, C. Leclercq, A. Lazarus, J. Mugica, P. Mabo and S. Cazeau, xe2x80x9cPermanent left-ventricular pacing with transvenous leads inserted into the coronary veinsxe2x80x9d, PACE, 21(1-ll), 239-245, 1998) describe clinical trials that had been conducted using a specially-developed coronary-sinus lead for this purpose.
Furthermore, thin catheters for acute catheterization are commercially available. These catheters usually use parallel-cables (not coiled) to achieve a small cross-section. However parallel-cable technology for chronically-implantable leads is still under development, since leads constructed in this technology may not be as robust and durable as those made using wire coils, and therefore require careful design to achieve the required reliability. Moreover, these leads do not have an intrinsic lumen for a guidwire or stylet, and thus require the development of new positioning techniques.
The closest geometrical configuration related to the present invention of which the inventor is aware is described in U.S. Pat. No. 5,755,766 (Chastain et al.). Named xe2x80x9cOpen-ended Intravenous Cardiac Leadxe2x80x9d, that patent discloses a lead which has a narrower distal end than the rest of the lead body. However, the change in the lead diameter is caused by the reduction in the lumen diameter, bringing no electrical or structural improvements to the design of the lead. Furthermore, in that patent there is a thin lead extension, which is deployable after the lead had been positioned. However, the lead extension of the lead described therein carries electrodes through conductors which maintain their diameter along the length of the catheter and must fit within the lumen of the lead (this may prove impractical, even for high impedance connections). Again, this option neither reduces the electrical resistance of the lead, nor does it improve the overall reliability of the lead.
To-date leads are built using conductors of constant-diameter. As such, the resistivity is constant along the lead. In contrast to that, in the present invention resistivity is maintained low along most of the lead, only increasing at the distal end, where reduced diameter lead is required to effectively catheterize the coronary sinus and coronary veins.
It is the object of the present invention to provide an improved intravascular lead for the delivery of electrodes suitable for use in coronary veins.
It is another object of the present invention to provide an intravascular lead that is relatively thinner at its distal end in its diameter with respect to known intravascular leads, thus allowing insertion of the distal end of the lead and delivering of an electrode in thinner coronary venules.
Yet another object of the present invention is to provide such an intravascular lead constructed at its distal end of tapered coated cables, thus imparting lower impedance and smaller diameter intravascular lead end than prior art intravascular leads.
There is thus provided, with accordance with a preferred embodiment of the present invention, an intravascular lead comprising a at least one electrode electrically connected to a conductive wire of a predetermined diameter, tapered at least at one predetermined location along said wire towards its distal end to provide a predetermined smaller diameter wire, thus presenting a main proximal relatively thick lead segment, and a relatively thinner distal lead segment, allowing catheterization of the cardiac sinus and in particular the delivery of said electrode into a selected coronary venule.
The tapering of the end of the wire renders the lead lower total impedance relatively to other prior-art leads.